The measurable brightness of the LED is a straightforward sum of the times it's on and the times it's off. Shift the ratio so it's off more than it's on and it

The measurable brightness of the LED is a straightforward sum of the times it's on and the times it's off. Shift the ratio so it's off more than it's on and it gets dimmer. The "fully bright" part is a consequence of human vision. Your brain is making sense of limited, noisy information coming from your eyes. A flickering light appears brighter than the light in steady state, lots of still images shown in rapid succession look like they're moving, as far as you can tell you can perceive the full range of colour out of the corner of your eyes, and the dress could be either colour.